The present invention relates generally to getters for removing hydrogen from sealed microelectronic packages, and the like, and more particularly, to a composite film hydrogen getter for removing hydrogen from sealed microelectronic packages backfilled with an inert gas, and to a metal foil or thin metal film hydrogen getter that catalyzes the reaction of hydrogen with backfilled air or oxygen.
The deleterious effects of hydrogen on the performance of various types of electronic devices, such as gallium arsenide (GaAs) and related compound semiconductor devices, is well known. Hydrogen is capable of entering the crystal structure of these materials and wherein band-gap trap states are formed that limit the carrier lifetime of the devices. Thus, compound semiconductor devices suffer degraded electrical performance when operated at normal operating temperatures in an atmosphere that includes hydrogen. Therefore, reliable operation of such devices requires the removal or exclusion of hydrogen from the surrounding atmosphere. In addition, ferroelectric materials such as strontium bismuth tantalate or strontium bismuth tantalate niobate, for example, are sensitive to and degrade in the presence of small amounts of hydrogen.
Strontium bismuth tantalate (SBT), bismuth strontium tantalate niobate (SBTN), lead zirconate titanate (PZT) and many high temperature superconductors containing bismuth are all sensitive to small amounts of hydrogen at elevated temperatures. Ferroelectric memory devices containing these materials have failed at temperatures of 125.degree. C. with less than 100 PPM hydrogen. The same parts are stable for extended periods at 125.degree. C. when exposed to air (0.5 PPM hydrogen). For military and for an increasing segment of the commercial market survivability at 125.degree. C. is mandatory.
The accumulation of hydrogen gas is particularly problematic in hermetically-sealed device packages. While hermetically-sealed packaging offers its contents protection against oxygen, water vapor, and other harmful contaminants present in the atmosphere, it also serves to retain and accumulate internally generated contaminants. Hydrogen outgasses from such devices and is accumulated within the hermetic packaging and invades semiconductor lattices of the device. Once in place, the hydrogen acts as a dopant that alters the response characteristics of the device in erratic ways. Hydrogen concentrations of 0.1% by volume (1000 PPM) dramatically alter the response characteristics of semiconductor devices, and hydrogen concentrations on the order of 0.5% by volume (5000 PPM) have been observed in hermetic packages after extended periods.
The present invention was developed specifically as a hydrogen gettering material for sealed microelectronic packages containing ferroelectric memory devices containing SBT and SBTN. While many vacuum gettering materials are commercially available and were evaluated for use, none were found to getter hydrogen sufficiently to protect the ferroelectric material. Conventional gettering materials do not work with sealed microelectronic packages primarily because they do not specifically getter hydrogen, but also getter other gases as well.
U.S. patent application Ser. No. 08/629,286, filed Apr. 8, 1996, entitled "Thin Film-Coated Foil Getters for Hydrogen in Electronic Device Packages" assigned to the assignee of the present invention provides for the use of a palladium (Pd) coated gettering metal, such as zirconium (Zr), titanium (Ti) for example, as a hydrogen getter. The gettering material disclosed in this patent application relies on the specificity of the clad (coated) material to diffuse hydrogen while not diffusing nitrogen or other elements, which permits the gettering metal to getter only hydrogen. These coated gettering metals were placed in sealed microelectronic packages backfilled with nitrogen and were tested, but they did not work sufficiently well to remove all the hydrogen from the sealed package in the presence of the nitrogen. Consequently, the electronic circuit in the microelectronic package degraded over time.
Powdered palladium oxide (PdO) has been used as a hydrogen getter material in dewars, for example. The difficulty with powdered palladium oxide gettering material is that the powder is loose in the package (i.e., not attached to the package). One embodiment of the present invention solves this problem. Another embodiment of the present invention capitalizes on the ability of certain metals to catalyze the reaction of hydrogen and oxygen to form water. Specifically this invention provides a palladium film in an oxygen containing package to getter the hydrogen by producing water.
Accordingly, it is an objective of the present invention to provide for a composite film hydrogen getter for removing hydrogen from sealed microelectronic packages backfilled with an inert gas. It is another objective of the present invention to provide for a metal foil or thin metal film hydrogen getter that catalyzes the reaction of hydrogen with backfilled air or oxygen.